The present invention relates to a method and apparatus for increasing process yields of data storage devices. The invention relates specifically to a technique for increasing process yields of magnetic disc drives.
Data storage devices in the form of magnetic discs consist of a collection of platters rotating on a spindle. The platters are metal discs and are covered with magnetic recording material (usually on both sides) to thereby provide a plurality of media surfaces to which data can be written and from which it can be read. Each media surface is divided into concentric circles, called tracks. The number of tracks varies depending on the design parameters for the disc drive. Each track in turn is divided into a number of sectors that can be used to store data. A sector is the smallest unit to/from which data can be read or written.
To read and write information into a sector, a movable arm containing a read/write head is located over each surface. At least one read/write head is provided for each surface. Each movable arm is typically linked to a servo controlled position mechanism capable of moving the head(s) in a radial or lateral direction over the recording surface.
A controller is used to access the discs on the drive and manage the flow of data between a computer system and the disc drive. The controller sends commands to move the read/write head into the correct position. A controller typically includes one or more microprocessors and memories to perform these tasks.
Variations in the quality of the head and media components coupled with manufacturing variations can often result in a sector, a number of sectors, or even a whole track of sectors, becoming defective.
In order to address the problem of defects in the media surface, the storage device is typically constructed to have a number of spare sectors which can be used to replace damaged sectors. Thus, in a drive, the total number of physical sectors equals the total number of logical sectors plus a number of spare sectors. Further, in order to address the fact that different read/write heads will have different read/write capabilities, a variable bits per inch (VBPI) tuning technique has been developed. VBPI tuning involves testing each head and assigning different read/write densities to the heads in accordance with their relative capabilities while still providing the required number of physical sectors.
Typically, in order to meet a pre-specified capacity, the design specifications for a drive specify the logical sector requirement required to meet the pre-specified capacity, together with a spare sector requirement based on an assumption regarding the likely number of defective sectors to be found in the drive.
The problem with the foregoing technique is that VBPI tuning does not take into consideration the number of spare sectors which will actually be needed in order to provide the designed for number of logical sectors. If there are too many defective sectors or tracks, there may be insufficient sectors to meet the design criteria, in which case the drive will fail to pass the test process.
Accordingly, it would be desirable to provide a technique which ensures that sufficient spare sectors are provided. It would be advantageous if such a technique also ensured that the risk of failure of any read/write heads was minimized. The present invention provides these and other advantages, and offers a solution over problems faced by the prior art.
Accordingly, one embodiment of the present invention provides a method of increasing process yields of data storage devices in which data is stored on a plurality of media surfaces, and at least one read/write head is associated with each media surface in order to read/write data from/to each media surface, the method comprising the steps of: (a) testing each read/write head in order to allocate a read/write density to each read/write head relating to the density at which each read/write head is capable of reading/writing data from/to a media surface; (b) determining whether said data storage device will have sufficient logical storage sectors to provide a predetermined data storage capacity for said data storage device if the allocated read/write densities are used in said data storage device; and (c) altering the allocated read/write density of at least one read/write head if necessary so as to ensure that said storage device has sufficient logical storage sectors.
Another embodiment of the present invention provides an apparatus for increasing process yields of data storage devices in which data is stored on a plurality of media surfaces, and at least one read/write head is associated with each media surface in order to read/write data from/to each media surface, the apparatus comprising: (a) first means for testing each read/write head in order to allocate a read/write density to each read/write head relating to the density at which each read/write head is capable of reading/writing data from/to a media surface; (b) second means for determining whether said data storage device will have sufficient logical storage sectors to provide a predetermined data storage capacity for said data storage device if the read/write densities allocated by the first means are used in said data storage device; and (c) third means for altering the allocated read/write density of at least one read/write head as necessary so as to ensure that said storage device has sufficient logical storage sectors.
Another embodiment of the present invention provides a data storage device which is using the above method.
These and various other features as well as advantages which characterize the present invention will be apparent upon reading of the following detailed description and review of the associated drawings.